1. Field of the Invention
This invention relates to the conversion of heavy hydrocarbon oils such as petroleum residua to more valuable liquid distillates by simultaneously cracking and hydrogenating the heavy oils in the presence of a hydrogen donor diluent.
2. Description of the Prior Art
It is known in the art to upgrade hydrogen deficient petroleum residua (resid) by thermally cracking the resid in admixture with a hydrogen donor diluent. The hydrogen donor diluent is a material, generally aromaticnaphthenic in nature, that has the ability to take up hydrogen under mild hydrogenation conditions and to readily release the hydrogen to a hydrogen-deficient resid under thermal cracking conditions. One of the principal advantages of the hydrogen donor diluent cracking (HDDC) process is that it can upgrade resids which are not readily amenable to other conversion processes, and further that it can provide high conversions in the absence of a catalyst and with a minimum of coke deposition. The cracked materials produced by the HDDC process are readily converted to desirable products, and the hydrogen donor diluent can be recycled through the hydrogenation step for reuse in the cracking unit.
The HDDC process is well known in the art, and a comprehensive description of the process, including materials, flows and operating conditions, appears in U.S. Pat. No. 2,953,513. Variations of the HDDC process, particularly as to the makeup of the hydrogen donor diluent, are described in U.S. Pat. Nos. 2,873,245 and 3,238,118. All of the prior art processes utilizing the HDDC step, as exemplified by the above-mentioned patents, blend the total diluent charge with the resid charge upstream of the cracking unit. While this technique has proved practical and has enjoyed commercial success, there has been a need for an improved HDDC process which achieves better hydrogen utilization. Such a process is provided by the present invention.